1. Field of the Invention
The present invention relates to a printing apparatus and a printing method for printing an image on an entire print medium by transporting the print medium relative to printing means that prints an image by forming dots on the print medium.
2. Description of the Related Art
Demands for digital image printing apparatus as output devices for a wide range of electronic equipment, including computers, copying machines and facsimiles, are growing significantly. The printing apparatuses currently in use are capable of using various print mediums, such as plain paper, OHPs and glossy paper. Information that can be printed includes various kinds of data, such as graph and pictures as well as general documents. Of the printing apparatus, an ink jet printing apparatus has come to be able to print images of high quality, even surpassing that of silver salt pictures thanks to a higher density integration of printing means and a color image printing capability that have become possible in recent years. Because of these advantages, there are increasing numbers of occasions where the ink jet printing apparatus is used for printing photographs.
With the picture printing application of the ink jet printing apparatus ever increasing, a so-called “marginless printing”, which prints an image on the entire surface of a print medium without leaving a margin edge along a periphery of the print medium, has come to be one of the important printing methods in the ink jet printing apparatus as in the case with silver salt pictures.
Among ink jet printing apparatus capable of implementing such a “marginless printing”, there is, for example, an apparatus disclosed in Japanese Patent Application Laid-Open No. 8-169155.
In an ink Jet printing apparatus disclosed in Japanese Patent Application Laid-Open No. 8-169155 (1996), a setting of print data for marginless printing is performed as shown in FIG. 10 and FIG. 11.
FIG. 10 shows how print data to be printed in one main scan of a print head is arranged in a main scan buffer, in a so-called serial type ink jet printing apparatus which performs printing by moving ink jet printing means (print head) having a plurality of print elements (or nozzles) in a direction perpendicular to a transport direction of the print medium. FIG. 11 shows how print data is set on the entire area of a print medium for the marginless printing.
When the printing is done in one main scan of the print head, it is necessary to store in a buffer data which indicates whether or not a dot is to be formed at each position arranged in the main scan direction at a pitch that matches a dot formation pitch for each nozzle.
The main scan buffer BF shown in FIG. 10 represents a case where the number of nozzles arrayed in the print head is V and the number of printed dots in the entire area of the print medium in the main scan direction is H.
In the figure, Hb1 and Hb2 indicate the number of dots to be formed in areas overrunning from the left and right side edges of the print medium (front and rear ends in the scan direction) when a marginless printing is performed. When the marginless printing is performed, those areas overrunning the print medium onto which ink is ejected need to be set for the following reasons.
When a print medium is supplied and transported, an actual position of the print medium may deviated from a theoretical position T0 set n the printing apparatus, as shown in FIG. 11. This positional deviation varies according to dimensional errors of components making up the printing apparatus that occur during the manufacturing process and to changes in conditions for supplying and transporting print medium that are caused by temperature and humidity variations. Therefore, these variations are difficult to eliminate completely.
If a marginless printing is performed with the print medium position deviated from a theoretical position and the printing operation (ink ejection operation) is performed only on the theoretical position of the print medium, an area overrunning from the theoretical print medium position fails to be applied with ink, forming a margin W. This indicates that the marginless printing is not performed properly.
Thus, in performing the marginless printing, it is conventional practice to set an overrunning area T2 where the printing operation is performed outside the periphery of the theoretical print medium position set on the printing apparatus, as shown in FIG. 11. As a result, should the print medium, after being supplied and transported, deviate from the theoretical position, this enables the entire print medium to be applied with ink. In FIG. 11, n represents an area printed by nth main scan and n1 an area printed by (n+1)th main scan.
In the ink jet printing apparatus disclosed in Japanese Patent Application Laid-Open No. 8-169115 (1996), however, a maximum value of positional deviation of the print medium is experimentally determined and a uniform overrunning area T2 of a width equal to the maximum deviation is set outside of and along the periphery of the theoretical print medium position. Normally, the width of the overrunning area T2 is set to about 1 mm to 3 mm.
With this arrangement the amount of ink applied to where the print medium does not exist tends to be comparatively large, causing a variety of inconveniences.
One such inconvenience is an increased running cost due to increased ink consumption. The ink consumption for one sheet of print medium is the amount of ink applied to the overrunning area added to the amount of ink applied to the entire surface of the print medium. Therefore, the larger the overrunning area, the higher the running cost based on ink consumption becomes.
Another inconvenience is a contamination of interior of the printing apparatus with ink. The ink jet printing apparatus for marginless printing has an ink absorber installed at the printing position so as to absorb that part of the ink applied to the overrunning area T2 which does not land on the print medium S. However, the print head produces minuscule ink droplets (ink mist) as well as normal-size ink droplets that land on the print medium S and the ink absorber. The ink mist is carried by an air flow produced by the main scan operation of the print head, floats around and eventually adheres to various parts other than the absorber, contaminating the interior of the printing apparatus. As the overrunning area T2 increases, the degree of contamination deteriorates.